It is desirable to use AC coupling between circuit stages e.g. amplifiers and mixers, in a receiver circuit in order to prevent unwanted DC signals caused by circuit DC bias voltages and mismatches from being propagated down the receiver chain.
It is also known to switch from a high coupling corner frequency, for rapid settling of a signal during preparation of data reception, to a low corner frequency, for low signal distortion during data reception, in receiver equipment with AC-coupled receiver circuits and AC coupling filters.
In receiver equipment with AC-coupled receiver circuits, where it is desired to switch from a high coupling corner frequency for rapid settling during e.g. amplifier gain programming to a low corner frequency for low signal distortion during data reception it is known that the properties of the signal are problematic when designing an AC coupling circuit for a signal with low frequency components during the preparation of data reception.
In practice this mean that the switched circuit suffers from a similar trade-off to the unswitched: in order to have reasonable settling times, it is necessary to have a reasonably high corner frequency when preparing for reception. However, the low frequency components of the signal mean that it is necessary to switch to a very much lower corner frequency for signal reception. The high initial corner frequency means that the coupling is sensitive to short term DC components, and the low final corner frequency leads to a very long settling time for the transient thus generated by the AC coupling switch.